Mill and process for autogenous grinding of friable material



Feb. 19, 1963 H. HARDINGE MILL AND PRocEss FOR AUToGENoUs GRINDING OF'FRIABLE MATERIAL 4 Sheets-Sheet l Filed June 24, 1959 INVEN TOR H/QZLOWL' HQ60/NGE ATTORNEY Feb. 19, 1963 H HARDINGE l 3,078,049

MlLI.. AND PROCES FOR AUTOGENOUS GRINDING Filed June 24, 1959 OF FRIABLEMATERIAL 4 Sheets-Sheet Z ATTORNEY Feb. 19, 1963 H. HARDINGE MILL ANDPROCESS FOR AUTOGENOUS GRINDING OF FRIABLE MATERIAL 4 Sheebs-Sheei'I 3June 24, 1959 Filed lII llllllllll II I I I 0 l l l l.

Feb. 19, 1963 H. HARDINGE 3,078,049

MILL AND PROCESS FOR AUTOGENOUS GRINDING OF FRIABLE MATERIAL. Filed June24, 1959 4 Sheets-Sheet 4 /22 //o /Zo//z l /36 /52 /40 /30 j /4-2 l j i/46 ATTORNEY 3,078,049 Patented Feb. 19, 1963 tice 3,078,649 MILL ANDPROCESS FOR AUTOGENOUS @BIND- ING F FRIABLE MATEREAL Hariowe Hardinge,York, Pa., assigner to Hardinge Cornpany, lne., York, Pa., a corporationof New York Filed .fune 24, 1959, Ser. No. 822,612 27 (Jiaims. (Cl.Zei-26) This invention relates to reduction of solid friable material,such as ore, non-metallic minerals, coal and the like from arun-of-the-mine condition including coarse lumps, intermediate andrelatively fine sizes to a desired range of fine particle sizes and,more particularly, to a process and mechanism to achieve such reductionin size, by autogenous grinding which, essentially, comprises causingthe material to grind itself, with or without the aid of auxiliary meanssuch as balls, rods or other aids within the mill.

Autogenous grinding, per se, is not new and a comprehensive review onthis general subject by the present inventor is found in the Engineeringand Mining Journal, June 1955, vol. 156, No. 6, at pages 84-90, entitledMalring Rock Grind Itself, and also in a paper presented before theAmerican Mining Congress entitled Autogenous Grinding and reprinted inthe American Congress Journal, pages 56-62, October 1958. Many of theproblems confronting the mining industry with respect to autogenousgrinding are discussed in said articles and, as of the publication datesthereof, the existing state of this art is described. The expressionautogenous grinding means in effect, self reduction, that is, thematerial undergoing reduction in effect reduces itself during thereduction process.

The present invention relates to improvements in both a method and millapparatus which solve many of the existing problems in autogenousgrinding but, in order Ithat such problems can be appreciatedadequately, some of the fundamental requisites of the operation of anautogenous mill for grinding and pulverizing ore, nonrnetallic minerals,coal and the like should be recounted preliminarily to form a basis forhighlighting and appreciating the advantages and details of theinvention which are set forth thereafter in this specification.

By the expression run-of-the-mine is meant a mixture normally of coarse,intermediate and fine sizes, the larger sizes being sufcient to reducethemselves along with the other sizes present, even though in some casescertain size ranges may be eliminated or partially treated separately.

There preferably should be a satisfactory ratio of fine and coarsematerial in an autogenous mill and process. The coarse material isessential to perform grinding of the intermediate and finer sizes untila desired range of fines are produced and are removed from the mill suchas for further processing, either chemical or physical. The presence ofsome of the finer particles at all times is desired to somewhat cushionthe coarse pieces relative to the mill while tumbling, thus minimizingabrasion on the liner of the mill and also somewhat retarding thedecreasing of size of the coarse pieces which are the principal grindingmedia for the smaller particles, whereby enough of the coarse materialshould be present to drop onto each other and the other smaller materialwith desired crushing effect to be gradually reduced to finer sizes. Thesupply of runofthemine solid raw material to the mill usually insures anadequate supply of the coarse material to effect desired pulverizing notonly of the coarse pieces themselves but also the intermediate sizes andfiner particles of material. The material which has been reduced to thedesired size is removed from the mill by any of a number of means, orcombinations thereof, including if desired, such auxiliary aids asgaseous or liquid fluid currents regulated as to volume and velocity toentrain desired ranges of fine particles and particularly if greaterspeed is desired, after the material has passed through a grate orperforated diaphragm which effects retention of the coarser materialwithin the mill and performs at least somewhat of a sizi-ng function.

During rotation of the autogeneous mill drum, the material therein iscarried upwardly mainly by friction and centrifugal action until gravityovercomes these forces and the material then drops or rolls down theunderlying material to provide a continuous tumbling action of thematerial in the mill. During such tumbling, the larger particles orlumps of material crush, grind, and ultimately pulverize the smallerparticles; they themselves gradually becoming broken by such action and,in turn, being ground by incoming larger pieces.

One of the difiicult problems in autogenous grinding comprisesmaintaining an adequately thorough mixture of all sizes of materialwithin the mill. There is a definite tendency for the material to becomesegregated due, primarily to .the natural phenomenon that when a mixtureof material, ranging in sizes from coarse to ne particles, is dischargedor dumped onto a pile, the coarser particles roll down the pile fasterthan the finer fraction with the result that more of the fines willremain nearer the top than the coarser fraction and the separate sizesthereby becoming segregated in such localities. This likewise occurswithin a rotating drum type mill for autogenous grinding, where, duringthe rotation thereof the cascading mass at the top of the load rolls andfalls down the incline formed by the tumbling action of the rotatingmass within the drum.

When fluid currents are passed through the mill from the feed end to theexit end, for example, there is a tendency for these additional currentforces to displace the material laterally, with the result that thelarger pieces will tend to remain adjacent the feed end, while the finermaterial is moved more easily and concentrates adjacent the exit end,whereby the overall mass is not distributed as it should be throughoutthe mill for effective autogenous grinding.

Another problem of considerable extent comprises the lifting of thematerial in the mill as high as possible, for a given speed of rotation,before it falls onto the material lower down in the mill to effectcrushing of boththe latter and the falling material. Attempts to achievemaximum lifting effects having included the employment of traus verselifting bars extending radially inward from the inner peripheral surfaceof the drum of the mill a distance adequate to receive therebetween thematerial to be lifted and retain the same while moving upwardly as highas possible before gravity causes it to fall therefrom.

Obviously, the longer the material can be retained between the lifterbars before it falls, the higher it will be lifted and the greater willbe the fall with resulting higher impact and longer distance of traveldown the slope of the moving mass. To increase the retention of thematerial and thus achieve a higher lifting effect, greater heights oflifting bars in a radial direction have been used, even including thosewith undercut faces in some instances, with the result that the materialfills the spaces between the bars to such an extent that movementtherein virtually stops as the mass is being raised during the upwardpath of the material near the periphery. This condition exists untiljust at the time it falls away at the top of the upward travel. In otherwords, a very high lifter in effect tends to decrease the effective andactive grinding volume and the active mass undergoing reduction tends toorbit and also slides over that stationary portion of the load heldbetween the high litters. Such a design which produces a high liftingaction tends therefore to defeat its own purpose.

The mills best suited for autogenous grinding comprise rotating drumsprovided with a feed inlet at one end and an exit at the opposite end,said inlet and exit preferably extending through hollow trunnions whichsupport the drum during rotation. In order that the most effective typeof grinding may be achieved, it is to be understood that the drums ofthe invention preferably should have a diameter compared to itseffective grinding length which .is considerably greater than has beenthe practice heretofore where special grinding media or bodies have beenemployed to grind pre-sized material as the feed.

The principal object of the invention is to provide an autogenous millof the type referred to above, and the `process of operating the samewhereby a susbtantial increase in the height of drop of at least thelarger material undergoing treatment will take place to produce moreeffective and efficient reduction in size of the material undergoingtreatment.

Another object of the invention is to'provide an autogenous mill and amethod of operating the same wherein thorough intermixing of all sizesVof material, especially laterally, takes place constantly during theoperation of the mill to minimize lateral segregation of the material.

A further object of the invention is to provide an autogenous mill and amethod of operating the 'same wherein `practical and relativelyfool-proof means are provided for lifting especially the larger materialundergoing treatment within the mill to substantially greater heightswithin the mill than was heretofore possible before the same `falls bygravity and such means for achieving such lifting of the material arereadily changeable for means of different sizes best suited forparticular types and sizes 'of material which are to be subjected togrinding and comminuting within the mill, whereby maximum efciency ofthe operation of the mill is achieved relative to any given run ofmaterial.

Still another object of the invention is to provide an autogenous milland method of operating the same wherein a discharge arrangement isprovided that is operable to permit the discharge of material at a levelbelow the trunnion exit of the mill, and the provision of means toprotect the discharge arrangement from undue abrasion as well as aid inthe lateral intermixing of the material within the mill.

Another object of the invention ancillary to the object immediatelydescribed above comprises the utilization of perforated diaphragmscreening means as Such discharge arrangement, said screening meansextending generally radially from the trunnionexit toward the innerperipheral wall of the mill but preferably spaced from said peripheralwall, there also being provided means to produce discharge of materialfrom the screening means through the trunnion exit of the mill.

One further object of the invention is to provide an tautogenous milland method of operating the same Whereby effective use is made ofconical ends in the mill not 'only to aid in lateral mixing of thematerial undergoing 'treatment to minimize segregation, but also to aidin effecting higher lifting of at least the larger sizes of material toproduce a more effective drop by more positive means than has heretoforebeen possible, such dropping of the material also being in a directedmanner to aid in achieving the lateral mixing of the material undergoing-treatment.

Still another object of the invention is to utilize a number of dierentembodiments of sloping inner surfaces on the peripheral wall of anautogenous mill in "order that such sloping peripheral inner surfaceswill cooperate with other structures and method of opera- `tion of themill to aid still further in achieving maximum, substantially uniformintermixing of the material undergoing treatment throughout the entiremass thereof while the mill is operating.

Details of the foregoing objects and of the invention, as well as otherobjects thereof, are set forth in the following specification andillustrated in the accompanying drawings comprising a part thereof.

In the drawings:

FIG. 1 is a side elevation, partly broken away and the broken away partbeing illustrated in vertical elevation, of one embodiment of autogenousmill having conical ends and in which the principles of the presentinvention are utilized.

FIG. 2 is a view similar to FIG. 1 but showing an autogenous mill havingparallel end walls and otherwise em bodying the principles of thepresent invention.

FIG. 3 is a sectional view of the mill shown in FIG. l, as seen on theline 3 3 of said figure, to illustrate an exemplary disposition of thematerial undergoing treatment within the mill, especially to show thelifting effect afforded by the mill.

FIG. 4 is a transverse sectional view of the mill taken within a planeparallel to the axis of the mill, on the line 4 4 of FIG. 3, but showinga slightly different form of peripheral liner than in FIG. 1 and also aslightly different height of lifting bars than those shown in FIG. l,said View primarily illustrating exemplary disposition of materialwithin the mill and especially the manner in which mixing of the varioussizes of material takes place especially in a lateral direction relativeto the end walls of the mill.

FIG. 5 is a fragmentary vertical section sectional elevation of stillanother embodiment of the invention similar to that illustrated in FIG.l and showing a section of another embodiment of the peripheral wall andscreening means of the mill.

FIG. 6 is a view similar to FIG. 5 showing a still further embodiment ofperipheral Wall and screening means in a mill otherwise basicallysimilar to the embodiment shown in FIG. l.

FIG. 7 is a vertical elevation of a mill drum embodying the presentinvention and similar to the embodiment shown in FIG. l but illustratingby exemplary arrows various paths taken by certain typical sizes ofmaterial within the mill while undergoing treatment therein.

FIG. 8 is a vertical sectional View similar to FIG. 7 but illustratingthe embodiment of the invention shown in FIG. 2 and showing by exemplaryarrows typical paths taken by various typical sizes of the materialwithin the mill drum While undergoing treatment.

FIG. 9 is a fragmentary vertical sectional view taken on the line 9 9 ofFIG. 1 and illustrating details of the liner members and the transverseperipheral lifting bars which maintain the liner members in operativeposition and also operate to lift the material within the mill drum,said lifting bars being illustrated in full lines to show one exemplaryheight thereof, and in dotted lines, showing another exemplary heightthereof, selectively to provide variable lifting effect to suit aparticular size range of material being treated.

FIG. 10 is a sectional view taken on the line 10 10 of FIG. 9, andshowing details of the preferred bolt means by which the lifting barsare held connected to the mill drum.

FIG. 11 is a fragmentary sectional detail of a portion of the gratestructure employed in the embodiment shown in FIG. 1, as seen on theline 1.1 11 of said ligure.

FIG. l2 is a fragmentary plan View of the embodiment shown in FIG. 5 asseen from the line 12 12 of said figure.

FIG. 13 is a fragmentary vertical elevation as seen on the line 13 13 ofFIG. l2.

FIG. 14 is a sectional view similar to PIG. 9 but illustrating anotherembodiment of liner and lifter means.

It is to be understood that the various illustrations shown in thedrawings primarily are intended to be exemplary and not restrictive. Inautogenous grinding and comminuting of material by a rotating mill drum,and particularly for purposes of achieving the elevating of thematerial, and especially the larger particlesof material, to fall ontoor roll down the uppermost surface of the main body within the mill toachieve desired reduction of size of all of the material within themill, it is preferred that the diameter of the mill drum be considerablygreater than the length thereof in an axial direction to provide arelatively narrow mill. Accordingly, all of the illustrated exemplaryembodiments of mill within the attached drawings are so dimensioned, itbeing understood that the length in an axial direction is the effectivelength of the inner surfaces of the lining elements within the mill andexclusive of the projecting hollow trunnions connected respectively tothe end walls of the mill drum and the effective diameter is thediameter of the exposed inner surfaces of the peripheral liner sectionsor members of the mill drum.

It also will be seen that mill drums having conical end walls as well asend walls which are substantially parallel to each other and transverseto the axis of the mill drum are illustrated inasmuch as at leastcertain of the embodiments of the invention are substantially equallyapplicable to both types of autogenous mills. In regard to otherfeatures of the invention however, the same are more effective in onetype of mill than the other and these distinctions will be described indetail hereinafter.

In most of the embodiments illustrated in the drawings, grate meanscomprising screening diaphragm means are provided adjacent one end wallof the mill drum, said yscreening means comprising an important featureamong a number of important features of the present invention. It is tobe understood that there are certain important features of the inventionwhich do not depend upon said screening structure however and areapplicable to autogenous mills in which no such screening structure needbe employed.

Referring to the embodiment shown in FIG. 1, the mill 1li is of theautogenous grinding type and comprising a cylindrical peripheral memberor shell 12, to the opposite ends of which conical end shell members 14and 16 are connected at the periphery thereof by any suitable means suchas welding, riveting, or the like to form a drum. Connected coaxiallywith central openings in the end members 14 and 16 are hollowcylindrical trunnions 18 and 20. It will be understood that thetrunnions 18 and 2t) are supported in suitable bearings such as thoseemployed for a ball and rod mill, such bearings not being illustrated inorder to simplify the illustration of the invention, and the mill 1t) issupported by such bearings for rotation about the axis of the trunnions18 and 20. The trunnion 18 comprises the inlet or entrance to the milland a feed chute 22 extends into trunnion 18 for purposes of feedingrun-of-the-mine material into the interior of the mill 19. Preferably, afrusta-conical entrance cone 24 is formed within the trunnion 18 toguide the material readily into the interior of mill 1li.

Coaxial with the trunnion 18 on the interior of mill 10 and extendingaxially inward therefrom is an annular conical abrasion-resistant ring26 providing a circumferential bulge projecting axially into the mill 10for purposes to be described. The ring 26 preferably is formed from aplurality of arcuate segments which respectively are secured to theinner surface of the end shell 14 by any suitable means such as bolts 2Swhich extend through the shell and receive external clamping nuts. Suchsegments readily andvquickly may be replaced by additional segments of adifferent size which, -for example, may project a greater distanceaxially into the mill such as indicated by the exemplary dotted lineillustration 26.

Also secured to the inner face of the end shell 14 are a plurality ofsegmental sections 30 of abrasion-resistant liner members which are madefrom material similar to that from which the segmental sections ofconical ring 26 are formed. Particularly for use in mills of appreciablediameters, it is preferred that the segmental sections ?0 be of a sizewhich permit convenient handling, especially for purposes of replacementor the substitution of different sections, whereby the sections 30preferably do not extend as single sections radially between the conicalring 26 and the peripheral shell 12 of the mill. Rather, one or moreadditional annular segmental sets of liner sections 34 are utilized andare positioned between the sections 3@ .and the liner members on theperipheral shell 12 to be described.

The liner sections 30 and 34 preferably are secured to end 14 byradially extending wedge and lifting bars 36 and 38 which wedginglyengage adjacent edges of the segmental liner sections 30 and 34 and aresecured to end 14 by bolts 32 having taper heads received incomplementary holes in the bars, the bolts extending through the variouscircular rows of holes in end 14. The bars 36 and 38 may be replaced bysimilar bars respectively identified as 36 and 38 of different heightthan the bars 36 and 3S, thereby adapting the mill to handling a sizerange of material of a different average composition from that ofanother to secure the greatest efficiency, as determined by inspectionof or as the result of tests made using the size composition of a run ofmaterial to be treated by the mill. In other words, the invention isconcerned with changing the contour of the mill to produce therein areduction characteristic which will result in the most efficientproduction of a range of fine sizes of product material at the minimumoverall cost of reduction of the material to said range of tine sizes.

The trunnion 2t? comprises part of the exit of the mill and has a grate40 comprising perforated screening means of one or more slots orsize-limiting openings associated therewith, as Well as a circularconical ring 42 which provides a circumferential bulge extending axiallyinward toward ring 26 for purposes to be described. A frustreconicalexit member 44, having an end wall 46 therein, is mounted to extendcoaxially into the reversely-angled conical exit shell 4S which projectsthrough the hollow exit trunnion 2t? in spaced relationship thereto. Theexit member d4 is carried by conical ring 42 as clearly shown in FIG. 1.Ring 42 is sectional and is clamped to the end shell by bolts 54 whichextend through the sections and spacer sleeves 56 arranged between thegrate members 40 and the inner surface of end shell 16. Preferably, thegrate 40 comprises a plurality of segmental sections having radialdivision lines therebetween.

As best shown in detail in FIG. 1l, adjacent edges of the sections ofthe grate 40 are connected to the end shell 16 by radially extendinglifter bars 60 which receive clamping bolts 62 which extend throughspacer sleeves 56 to maintain the grate 46 in desired spacedrelationship from the liner plate 58 and end shell 16 of the mill.

Preferably the radially extending lifter bars 60 have beveled sides 64,as shown in FIG. 1l, which are complementary to adjacent side edges ofthe sections of the grate 40 whereby when said bars 60 are clamped intooperative position by the bolts `62, firm wedging-type clamping of thegrate sections 49 will take place. As also shown in FIG. ll, the radiallifting bars 60 which clamp the grate sections 40 may be replaced byother lifting and clamping bars 60 of different height as illustrated indotted lines. Said radial lifting bars 60 clamp the various gratesections into operative position.

Another segmental annular ring 66 having a conical inner surface isclamped against the inner surface of end shell 16 as shown in FfG. 1,said ring forming the periphery of an annular chamber 68 within whichthe material passing through the slots or openings of the grate 40 isreceived and from which discharge is effected by means to be described.Ring 66 is secured to the end shell 16 by bolts 70. The detachablesecuring of the annular ring 66 to the end shell 16 permits said ring tobe replaced by a ring of diffeernt height.

Positioned between the annular bulge ring 66 and the liner means withinthe cylindrical shell 12 are additional segmental liner members '74secured to end 16 by radial wedge bars 76 which are bolted to end 16 bybolts 78 similar to bolts 32 and 36. The detachable mounting of thewedge bars 76 permits the same to be substituted by other bars ofdifferent heights, as indicated by dotted lines 76 in FIG. 1. Linersections 74 and ring 66 define an annular space within the millcomprising an expanding zone 79 for purposes to be described.

Liner elements also are detachably connected to the inner cylindricalperipheral wall of shell 12 of the mill 10 and such sections, in thisembodiment of the invention, are formed and positioned so as to slopefrom the end members of the mill axially inward and radially outwardtoward the shell 12 of the mill. Even a gradual slope of a few degreesis highly effective. In this specific illustration of FIG. 1, it will beseen that a plurality of central liner sections St) are secured bytransverse wedge and lifting bars 82 affixed to shell 12 by bolts 84similar to bolts 32, 36 and 78, The bars 82 may be replaced by otherwedge and lifter bars 82 of a different height and the sections 80 thusare wedgingly clamped thereby in endtoend relationship around the innerperiphery of shell 12. 4Bars 82 readily may be replaced by other barswith substantially no disturbance to liner sections 80.

Oppositely sloping liner sections 86 are disposed between the oppositeedges of the liner sections 80 and the liner sections 34 and 74respectively adjacent the opposite shell ends 14 and 16. The sections 86may be maintained in such sloping relationship by filler members 88 suchas wedge-shaped pieces of wood. The sections 86 are secured to shell 12by wedge and lifter bars 90 which are shaped to extend substantially incontinuation, or otherwise, to the bars 82 and the bars 90 are securedto the shell 12 by bolts 92. As in regard to the other liner sections ofthe mill 10, wedging and lifter bars 86 may be replaced by other bars90' of a different height.

In the preferred operation of the mill 10 as shown in FIG. 1,run-ofthemine material is introduced through feed chute 22 at a rate inaccordance with the grinding rate of the mill. As said material isreduced in size, that which is reduced sutciently fine to pass throughlthe slots of the screening means 40 is discharged therethrough intoannular chamber 63. As the mill revolves, the material within said spacewhich is above the axis of the mill will fall onto the conical exteriorof exit member 44 and slides down the same to be discharged through theexit shell of discharge spout 4S. Lifting of the material within thechamber 68 is accomplished by the provision of lifting means such asplates 94 which extend from the annular ring 66 radially inward towardthe axis of the mill to preferably near the outer end of Athe exitmember 44 as shown in FIGS. 1 and 3. Such lifting action is furtherfacilitated if such plates 94 are curved so as to comprise spiral scoops95 as shown in FIG. 3.

The grinding and comminuting action which takes place within the mill1t) is best illustrated in FIGS. 3, 4 and 7. It is preferred that in theoperation of the mill, grinding and treating of the material be of anautogenous nature and that run-of-the-mine material be ground andreduced in size to a desired range of ne material for desired purposes,the largest of which are determined by the openings in the screeningmeans 40. It has been found that, contrary to previous attempts, the useof relatively low, as distinguished from' relatively high transverselifter bars or ribs S2 operate more effectively tomaintain relativemotion between the various size ranges undergoing reduction than whenthe lifter bars are higher than need be to prevent undue slippageagainst the peripheral shell liners, particularly when utilizing radiallifter bars in association with the end liners, which radial bars extendalong the interior of the ends of the mill. Hence, the radial liftingbars 36 and 3S at one end of the mill cooperate with the radial liftingbars 60 and 76 on the opposite end of the mill and, in view of the factthat the length or axial dimension of the mill is relatively short inproportion to the diameter thereof, a substantial quantity of coarse ma-*but of the material of the mass which it contacts.

terial within the mixture being treated will be elevatedto a pointhigher than the same ordinarily would take place if relatively hightransverse lifter bars 82 were used. The disadvantage of usingrelatively high transverse lifter bars which project radially inwardfrom the cylindrical shall 12 is that part of the mass of the materialwithin the mill tends to become locked and relative movement betweensaid lifter bars ceases or at least to such an extent that the majorportion ofthe spaces between the bars are filled with dead material andthe bars then have substantially no lifting effect upon the largersegment of the material and the effective grinding volume of the mill isreduced thereby. As a result, when such relatively high transverselifter bars are used, much of the material tends to orbit within therotating mass of the material directly above the innermost edges of therelatively high transverse lifter bars and is not carried as high withinthe mill as it would be if bars were employed only of sufficient heightto discharge lthe material onto the top of the mass so as to preventslippage against the shell liners by the size characteristics of thematerial undergoing reduction. A different average size piece of themass undergoing reduction calls for a different size lifting effect.Hence, the height of the bars should be subject to adjustment andtesting at minimum expense for operation of the mill at optimumeiciency.

By the use of relatively low transverse lifter bars 82 in conjunctionwith radial lifterbars on the end shell mem- Ibers of the mill,particularly where the heights of the radial lifter bars are selected inaccordance with the overall composition of the material, substantiallyfirm lodgment of the material taltes place between the transverse lifterIbars 32. Moreover, there is a tendency especially for the coarserparticles of material when falling or rolling down the sloping masswithin the mill to become momentarily held on the radial lifter bars sothat they are elevated to a higher position within the mill thanheretofore possible, even though some of the finer material may fallfrom between the coarser material, until finally, as illustrated inexemplary manner in FIG. 3, the coarser material is freed by gravityfrom between the radial lifter bars so that it falls and effects impactupon tthe sloping mass of the material within the mill, the most ofwhich, at that instant, is substantially stationary to receive maximumimpact, such coarser material also rolling `down the upper surface ofthe mass to effect reduction not only of itself Of equal, if not more,importance is the fact that such operation maintains a thoroughintermixing action of all sizes laterally, a condition that is importantto maintain in an autogenous grinding mill of the type here described asopposed to the desired classification for best operation oftheconventional ball or pebble mill.

It is diicult to illustrate or indicate exactly 4the motion of thevarious segments or particles of material within the mill but an attempthas been made to do this somewhat diagrammatically in FIG. 7, which isat a right angle to 'the view in FIG. 3, and wherein the release of thelarger pieces in particular from between the radial lbars 36, 38 and 60,76 is denoted by the arrows 96. When said larger particles, as well assome of the smaller particles fall from between the radial bars or ribs,they will engage the sloping annular surfaces or bulges 98 of rings 26and 42, whereby the falling material will be deflected toward the centeras indicated by the arrows 100. Such deflection of the material willtend to direct it toward the center of the mill while other materialwill be falling substantially directly downward, the falling materialcolliding to some extent with itself, whereby even further distributiontakes place throughout and particularly transversely across the 4mass ofthe material in the direction of the axis of the mill as is evident inexemplary manner in FIG. 4.

Particularly in regard to the material which rolls down -the slopingsurface of the mass of the material within the mill, when at least someof the larger pieces of said rolling material stop rolling adjacent the'instantaneous Abottom of said mass of material, the sloping surfaces ofthe peripheral liner sections 86 will tend to direct said materialtoward the center of the mill. Such material also includes the larger,faster rolling pieces especially, and these will be trapped between thetransverse ribs or bars 82 and be covered by the oncoming mass ofmaterial, whereby said pieces will not be released for dropping orrolling until they have been elevated to a relatively high positionwithin the mill so as to be free either to drop onto the mass or rolldown the same, some pieces rolling more or less centrally, while otherparticles thereof will tend to roll toward the feed or discharge end ofthe mill because of the tendency of the mass of the material to assumean angle of repose while being constantly moved by tumbling within themill, whereby such rolling down the sides of the mass will take placefrom the theoretical crest of the material within the center of themill. At least some of the larger particles will become momentarilyentrapped between the radial bars or ribs along the ends of the millduring such rolling and falling thereof, whereby a thorough mixing ofboth large, medium and small segments takes place.

An additional lifting effect is achieved by reason of some of thematerial being momentarily wedged or entrapped by the undercut surfaces98 of the rings or bulges 26 and 42, see FIGS. l and 7, so as to insurerelatively high elevation of such material before being overcome by theforce of gravity so as to cause the same to drop or roll relatively tothe tumbling mass of material in the mill. Still further, momentaryentrapment is afforded by the undercut surfaces of the annular ring 66which produces a similar effect to the undercut surfaces of rings 26 andt2 but in an area closer to the periphery of the mill. Additionallyhowever, the undercut surfaces of the ring 66 on that portion in theupper part of the mill assures deflection of the material, as indicatedby the arrows 96 in FIG. 7, away from the grate surface 40 when theelevated material falls so as to minimize abrasive contact of thematerial with said grate surface. Likewise, the sloping surface of theannular ring 42 nearest the axis of the mill deflects falling materialfrom the grinding Zone of the mill as well as that which falls or flowsagainst end member 44 and wall 46 such as shown, for example, in FIGS. land 4, toward the center of the mill and away from said grate so as toprotect the surface thereof from direct impact by such falling material.The radial bars 60 which extend across the grate 40 likewise aid inprotecting the grate from abrasive action, in addition to aiding inelevation of the material. Hence, passage of material through the slotsor other openings through the grate takes place primarily from rollingaction of the mass of material as distinguished from impact against thegrate.

From the foregoing description, especially with reference to FIGS. 3 and7, it will be seen that the operational results of the mill produce athorough mixing of the coarse, intermediate, and fine segments of thematerial as it is rolled and tumbled within the mill and before theparticles are submerged by the oncoming mass. The ability to change thevarious lifter bars and particularly those sections adjacent the ends 14and 16 of the mill for bars of different heights permits the mill tooperate effectively upon a wide range of size compositions ofrun-of-the-mine material. Accordingly, the mill is provided with radialand/or transverse lifting bars of desired heights after making apreliminary inspection of a run of material to be treated by the mill.Further, the conical ends of the mill, as shown in FIG. 1, offeradvantages over the parallel ends in the embodiment shown in FIG. 2, dueprimarily to the natural spreading effect afforded by the conical endswhich taper axially toward the peripheral section 12 of the mill,whereby the rolling material naturally tends to spread and then contractmomentarily during rolling and tumbling down the slope 10 of materialwithin the mill and as it hits the tapered liners of the shell 12. Thewhole mass is then inescapably being somewhat wedged between the slopingend walls which are relatively near to each other as distinguished fromthe relatively far apart end walls in a conventional ball or pebblemill.

Referring to the embodiment 'basically illustrated in FlG. 2, whereinthe mill 102 has a cylindrical peripheral member or shell 104 andparallel end members 106 and 108 which comprise large discs which arecentrally apertured and the peripheries of which are secured by weldingor otherwise to the opposite ends of the cylindrical shell 104, saidmill is supported at opposite ends by hollow trunnions 110 and 112 whichcorrespond and function similarly to trunnions 1S and 26 respectivelyshown in FIG. l. It will be understood that many of the details shown inFIG. 2 correspond to similar details shown in FIG. l, whereby suchdetails will not be described as minutely as in regard to the structureshown in FIG. l, reference being had where convenient to the detailsconcerning FIG. l.

A feed chute 114 extends into entrance `trunnion 110 and a reverselyangled conical exit shell 116 is connected to the end wall 108 andextends through exit trunnion 112. Annular rings or bulges 118 and 120,formed similarly to the rings 26 and Li2 respectively of the embodimentshown in FIG. l, extend around the central openings in the end walls 106and 168 respectively and are attached by suitable bolt means for readyreplacement and substitution. A frustro-conical exit member 122 ismounted in operative position concentrically with the exit shell 116 andin spaced relationship thereto.

The interior of the end wall 106 supports segmental liner plates 124 and126 respectively clamped to end 106 by bars 12S and 134B which serve asradial lifter bars in similar manner as the bars 36 and 38 of theembodiment shown in FIG. l. The lifter and wedge bars 128 and 130readily are replaceable due to conveniently being held in operativeposition by bolts 131 clearly illustrated in FIG. 2, whereby otherlifter and wedge bars 128 and 130 having different heights than bars 128and 130 may be mounted upon the end member 106. While wedge bars aredescribed and illustrated in the various embodiments, it is to beunderstood that any type of separate clamping bar will also serve thesame clamping purpose.

The end member 163 supports an annular grate 13-2 comprising aperforated diaphragm screening means which is illustrated as beingsubstantially parallel to end member 168 and is supported in spacedrelationship thereto by spacer sleeves 134. Radial lifter and clampingbars 136 preferably wedgingly clamp the segmental sections of the grate132 in spaced relationship to the end lmember 108 to provide an annularchamber 138 to receive the material which has been reduced to asufficient state of ineness that it passes through the slots or otheropenings in said grates. The radial bars 136 are replaceable by bars ofdifferent heights as indicated for example by the dotted line 136'.Another annular ring 148', similar in structure to ring 66 of FIG. l,defines the periphery of annular chamber 138 and also provides anundercut surface 142. The ring 140 is secured to end member 168 'bytaper head bolts 143.

End member 10S also supports additional segmental liner sections 144secured to the end member by radial lifter and wedge bars 146 which areconnected to end 103 by taper head bolts, whereby the same may bereplaced by other radial lifter bars 146 of different height, asdesired. The cylindrical shell 104 of the mill 102 is linedintermediately of the edges thereof by liner segments 14S which aresecured to the shell by transverse lifter and wedge bars 150 extendingsubstantially in parallel relationship to the axis of the mill, the bars150 being secured detachably by taper head bolts to the cylindricalshell 104,

11 whereby the same may be substituted by lifter bars having a differentheight.

Disposed between each end of the mill and the opposite ends ofthetransverse liner segments 148 are sloping liner segments 152 securedby lifter and wedge bars 154 which extend in the same general directionas bars 150 and may be replaced by bars of different heights. Further,it will be noted from FIG. 2 that the lifter bars 150 as well as thesegments 148 slope upwardly and outwardly -from the center thereof asseen in the lower part of the mill, whereby the associated linersegments connected to the cylindrical shell 104 provide oppositelysloping surfaces extending inward and radially outward from the axis ofthe mill, preferably at a gradual angle but which angle nevertheless isadequate to eifect lateral motion of the various sizes of materialwithin the mill during the rotation thereof, such lateral motionprincipally being toward the center of the mill.

The annular rings 118 and 120 serve to deect falling material toward thecenter of the mill in a similar manner to that performed by rings 28 and42 of the embodiment shown in FIG. 1. The ring 120 additionally protectsthe grate 132 from direct impact by falling material, while that portionof the additional ring 140 in the upper part of the mill serves todeflect falling material away from direct impact with grate 132 and,further, that portion thereof in the rising side of the mill affordslimited wedging action of material within the mill while rotating,whereby at least some of the material and particularly the largersegments thereof are elevated to a relatively high position within themill before gravity causes the same to drop or roll against the slopingmass of material within the mill.

In operation, the embodiment shown in FIG. 2 is illustrated essentiallyin FIG. 8, wherein exemplary arrows have been placed to illustrate in adiagrammatic manner what is observed to be approximate paths of certainseg- -ments of the material within the mill during the operationthereof. The embodiment shown in FIGS. 2 and 8 primarily relies foreffective lifting upon a cooperation between the transverse lifting ribsor bars 150, 154 and the radial lifting ribs or bars 128, 130 at one endof the mill and radial lifting bars 136, 142 and 146 on the grate andopposite end of the mill, which lifting bars have been selected by testor otherwise as to height for greatest elieiency relative to a certainrun of material. Thus, at least some of the larger segments of thematerial will become stationary momentarily particularly between theradial lifting bars or ribs so as to insure substantial elevationthereof within the mill before they are released by gravity to fall orroll onto the mass of material in the mill, such falling movement beingindicated by the arrows 156. As the material is dislodged from betweensaid radial ribs, at least some of the same may strike the annular ringsor bulges 118 and 140, being deflected thereby toward the center of themill. Still other large and intermediate, as well as some finer segmentsof the mass will be carried by the transverse lifter bars 150, 154 to asubstantial height within the mill, and drop more or less centrally inthe mill as indicated by the arrows 158. Such -falling material willroll down the upper surface of the sloping mass of the material and someof the larger elements, because of the angle of repose phenomenon, willroll toward the radial lifter bars, and rest therebetween until theyagain are released as the rotation of the mill brings them to the top ofthe load.

As treatment of the material continues, while thorough mixing thereoftakes place especially in a transverse direction parallel to the axis ofthe mill, falling material is deected from contact with the gratescreening means 136 but passage of relatively tine material through thegrate takes place in a manner similar to that described relative to FIG.l, above, including lifting of the material Within the chamber 138 byplates 162 or the like, for discharge '12 onto the conical surface ofexit member 122, as indicated by the arrows i.

Except for the increased holding, spreading and mixing action affordedby the conical ends of the embodiment of the invention shown in FIGS. 1and 7, the embodiment shown in FIGS. 2 and 8, wherein the ends of themill are substantially parallel to each other and perpendicular to theaxis of the mill, is capable of performing a number of the benecialresults of the embodiment shown in FIGS. l and 7 insofar as autogenousgrinding is concerned.

Referring to FIG. 5, a slightly different embodiment of millconstruction from that shown in FIGS. 1 and 9 is illustrated,particularly in regard to the transverse lifting ribs or bars adjacentthe periphery of the mill and the disposition of the grate relative tothe end member nearest the exit trunnion. The same basic referencecharacters are used in FIG. 5 as in FIGS. l and 9 for the elements whichare common to both embodiments. In the embodiment of FIG. 5, it will beseen that the grate 40, rather than being substantially parallel to theend 16 of the mill, is perpendicular to the axis of the mill, therebyaffording an annular chamber 164 of somewhat greater capacity than theannular chamber 68 in the embodiment shown in FIGS. 1 and 7. Thisembodiment necessitates the employment of spacing sleeves 166 ofgraduated lengths. Further the angle between the grate and opposite endof the mill in the embodiment shown in FIG. 5 is less than in theembodiment shown in FIGS. 1 and 7, whereby somewhat greater momentarywedging or compacting of the material takes place in the embodiment ofFIG. 5 as it rolls and falls toward the bottom of the mill duringrotation thereof as compared with the embodiment shown in FIGS. l and 7,thus enhancing the lifting of the material by the structure in FIG. 5before the material falls.

The liner segments 168 are held in position by transverse lifter andwedge bars 172, as shown in detail in IFIGS. 12 and A13. Bars 172 have asubstantially straight upper surface and are secured to shell 12 byclamping bolts 174. Similar lifter bars 176 are disposed between theliner segments 170, the ends of the lifter bars 176 nearest the lifterbars 3S and 76 respectively and preferably being shaped to mergetherewith. Bolts 174 secure the lifter bars 176 detachably to thecylindrical shell 12. 'Ihe straight upper surface of lifter bars 172 and176, in conjunction with the sloping surfaces of the liner segmentsatford greater lifting capacity than the arrangement shown in FIGS. 1and 2, due to the greater areas of the lifter bars -in the centersthereof than at the ends of the bars.

A still further embodiment is illustrated in FIG. 6, this embodimentbeing similar in some respects to that shown in FIG. 5 and also beingrelated to that shown in FIGS. 1 and 7. In FIG. 6, it will be seen thatthe feature which is principally different comprises the grate structureor screening means. There has been added in FIG. 6 an additional grateor screening member 178 which is substantially perpendicular to the axisof the mill 10, while the screening section 40, which is similar to thatshown in FIGS. 1 and 7, also is employed. Such disposition of screeningmeans close to the periphery of the mill places said means adjacent thelocation of maximum impact of the falling coarse pieces with the bed ofthe material, especially when the mill is loaded relatively lightly.This increased grate or screening area permits an increased rate ofremoval of the finer particles of material from the coarser pieces whichare retained within the mill for further processing. The screeningsection 40 is connected to the end shell 16 by means similar to thatshown in FIGS. l and 7, while the screening secetion 178, whichpreferably is formed from similar segments, is secured t0 the end shell12 by radial lifter and wedge bars 180 which extend in wedgingrelationship between adjacent edges of the segments of the grate section178. The relationship of the lifter bars 60 and 180 to the lifter bars36 and 38 on the opposite end of the mill will afford a variation inwedging of material therebetween over that shown in the precedingembodiments.

The radial clamping bars lll are secured against the segments of gratesection 178 by bolts lZ which extend through spacer sleeves 184.

It will be seen therefore from FIG. 6 that in addition to the annularchamber 68 between conical ring 42, grate screening means 4t? and endshell i6, an additional annular chamber lS extends between the gratemeans l't and end shell 16 and communicates with annular chamber 63 tocomprise an extension thereof, thereby affording an even greater annularchamber into which the liner particles of material may pass than thatafforded in the embodiment sho-wn in FIG. 5. To provide desired liftingeffect within chamber E38, the radial plates or scoops 9d in chamber 68preferably are supplemented by scoop-like members 95 within chamber 188which are similar in shape, as viewed from the end, to the scoops 95shown in FIG. 3, which facilitate the rate of travel of material behindgrate 173 to discharge cone dft when the mill is running at relativelyhigh speed.

While the various foregoing descriptions of the several embodiments ofmills illustrated in the different figures of vthe drawings haveincluded lifting bars which are searable from the lining segments of themill, it is to be understood that the lifting within the mills may beeffected by bars or ribs 19t) which may be integral with the linersegments 192 as illustrated in exemplary manner in FIG. 14, which is avertical sectional view similar to FIG. 9. Bolts 194 are used to securethe segments 192 to the shell 12' of the mill. It is to be understoodthat the segments i922 may be replaced by other segments having ribs 190of different'height than ribs 19d, thereby to vary the lifting effectsof the ribs. The height of the ribs is selected in the same manner asthat employed to select the detachable lifting bars of the otherembodiments described hereinabove.

Whereas a conventional conical mill straties the material in accordancewith the intended purpose thereof to achieve its desired objectives, thepresent invention utilizes, in at least several embodiments, sloped endssomewhat similar to a conical mill but prevents stratification of thematerial therein through the employment of a relatively narrow mill,applying specific deflecting means, using radial and transverseretaining and lifting bars on ends and peripheral shell of mill, as wellas annular expansion spaces extending axially outward of mill on atleast one end. By means of these, individual pieces or particles ofmaterial are caused to have lateral movements between the ends andassume no regular, repeated or stratifying lateral paths, therebyresulting in relatively uniform mixing and dispersion of all sizes ofmaterial throughout the mass in the mill. As an example of typical pathsof certain exemplary particles, reference is made in FIG. 4 in whichvarious typical large or coarse pieces of material are shown movingthrough certain typical paths, said pieces being numbered l1. through toshow progressive positions thereof within the mill and mass of materialtherein.

In the embodiments of the invention described in detail above, nospecific reference has been made to fluid currents which may be employedwith such embodiments to enhance removal particularly of the finerparticles of material from the mill. When the end wall 46 in FIG. l, forexample, is employed in the exit end of the mill, liquid currentsreadily may be circulated within the mill to eect wet grinding andenhance the flowing of at least the finer particles through the gratescreening means of the mill. If screening means is not employed, theexit end of the mill may be modied, especially to provide a passage tothe hollow exit trunnion, so that flowing of the material entrainedwithin the discharging liquid may take place. lf gaseous currents are tobe employed to circulate through the mill, especially to entrain thefiner particles and carry them from the mill, the exit end of the millcan be modified to permit this such as by omitting end Wall 46 andarrange an entrance end of a conduit relative to the exit trunnion ofthe mill, whereby either a negative or a positive pressure fluid currentmay be imposed upon such conduit in a direction to effect removal of thefluid current and entrained material from the mill through the yexittrunnion in accordance with well known principles. .Because of theconstant, through mixing of the material within the mill arrangement asherein specified, when either a liquid or gaseous current is circulatedthrough the mill, no objectionable stratification of the material willtake place as is otherwise the case where fluid currents are employed.The so-called stratifying or classifying action caused by fluid currentor other means is in fact a desirable feature when separate grindingmedia other than the material itself is employed such as in theso-called standard ball, pebble, or rod mill, but is not desirable inautogenous grinding of the type described hereinabove.

While the invention has been described and illustrated in its severalpreferred embodiments, and has included certain details, it should beunderstood that the invention is not to be limited to the precisedetails herein illustrated and described since the same may be carriedout in other Ways falling Nithin the scope of the invention as claimed.

I claim: 1. A rotatable tumbling mill for treating friable material toreduce the size thereof and having opposed ends of lconvex congurationssloping away from each other from Athe inner surface of said screeningmeans being exposed to the material undergoing reduction and the outerperiphery of said screening means being spaced inwardly from the outerperiphery of the grinding zone of the mill, and deflecting meansadjacent the outer periphery of said screening means having asubstantially annular deecting surface extending angularly inward awayfrom the exit end of the mill contiguous to said screening means andtoward the axis of rotation of the mill, said annular deilecting surfacebeing operable to be engaged by material falling within the mill anddeect the same away from said screening means to protect the same andalso to produce an added intermixing action upon said material withinsaid grinding zone.

2. A rotatable tumbling mill for treating friable material to reduce thesize thereof and having opposed ends of convex configurations slopingaway from each other from the periphery to the axis of the mill and thediameter of the internal grinding Zone of the mill being substantiallygreater than the axial length thereof, the ends of the mill beingprovided respectively with substantially coaxial inlet and exit openingmeans and the interior surface of the end having said exit means beingprovided with an annular space extending axially away from the center ofthe mill adjacent the periphery thereof and extending radially inwardtoward the axis a predetermined distance to provide a laterally expandedgrinding Zone in said mill, and perforated screening means carried bythe exit end of the mill and positioned at least partially opposite thegrinding zone of the mill and converging radially toward the exitopening means of the mill from the inner periphery of said annularexpanded zone, the circumferential surface of said screening means beingexposed to the material undergoing reduction to deflect the same awayfrom said screening means toward the center of the mill to minimizestratication of material within said grinding zone.

3. A rotatable tumbling mill for treating friable material to reduce thesize thereof and comprising a drum having opposed ends connected by aperipheral shell means and said ends respectively having substantiallycoaxial inlet and exit means therein and the interior of 'said drumdefining an internal grinding zone having a substantially greaterdiameter than the length thereof in an axial direction, perforatedscreening means carried by the end of the drum having exit means thereinand extending radially into the grinding zone, the circumferentialperimeter of said screening means being of lesser diameter than that ofsaid grinding zone and exposed to the material undergoing reduction, anddefiecting means extending angularly in an axial direction into thegrinding zone adjacent the outer periphery of said screening means andbeing operable to deect falling material from direct impactingengagement with said screening means, thereby minimizing abrasion ofsaid screening means and effecting mixing of all size segments ofmaterial in a transverse direction within said grinding zone.

4. A rotatable tumbling mill for treating friable material to reduce thesize thereof and comprising a drum having opposed ends respectivelyhaving substantially coaxial inlet and exit means therein and definingan internal grinding zone having a substantially greater diameter thanthe length thereof in an axial direction, the end of the mill having theexit means therein being provided with an annular recess extendingbetween the periphery fof the drum and extending radially toward theaxis thereof a predetermined distance and also extending axial- 1youtward from the center of the mill to provide a laterally expandedgrinding zone, and perforated screening means converging radiallyinwardly from the inner periphery of said expanded zone toward the axisof said drum, the inner surface of said screening means being exposed tothe material undergoing reduction and the surface comprising said innerperiphery of said expanded zone projecting in an axial direction intosaid mill and being operable to deflect material from direct impactingengagement with said screening means, thereby minimizing abra- 4`sion ofsaid screening means and effecting mixing of all size segments ofmaterial in a transverse direction within said grinding zone.

5. A rotatable drum-type mill for subjecting friable material toreduction of size and having ends thereon, the diameter of the interiorof the mill being substantially greater than the length thereof in anaxial direction and said ends having substantially coaxial inlet andexit means for material fed to and discharged from said mill, wearresistant lining means extending around the interior of said mill, thesurfaces thereof defining the inner periphery of said mill slopingradially outward from the perim- `eter of the ends of the mill towardthe center of the mill,

whereby material falling upon said peripheral lining means laterallyoutwardly from t-he center thereof will move toward the center of themill, and lifter bars extending radially inward from and transverselyacross said peripheral lining means at spaced circumferential intervals,said bars having substantially straight inner surfaces exposed to thematerial undergoing reduction, thereby providing transverse pocketsincreasing in depth from the outer ends toward the centers thereof.

6. A rotatable drum-type mill for subjecting a range of sizes of friablematerial to self-reduction of all sizes simultaneously and havingopposed convex ends sloping 'away from each other from the periphery tothe axis of the mill, the diameter of the interior of the mill beingsubstantially greater than the length thereof in an axial direction andsaid ends having substantially coaxial inlet and exit means for materialfed t-o and discharged from said mill, wear resistant lining meansextending around the interior of said mill, the surfaces thereofdefining the yinner periphery of said mill sloping radially outward fromthe perimeter of the ends of the mill toward the center of the mill,whereby materia-l falling upon said peripheral lining means laterallyoutward from the center thereof will move toward the center of the mill,and lifter bars extending radially inward from and transversely acrossi6 said peripheral lining means at spaced circumferential intervals,said bars having substantially straight inner surfaces exposed to thematerial undergoing reduction whereby the greatest lifting area of saidbars is substantially in the center of the mill.

7. A rotatable tumbling mill for treating friable material to reduce thesize thereof and comprising a drum having opposed ends respectivelyhaving substantially coaxial inlet and exit means therein and definingan internal grinding zone having a substantially greater diameter thanthe length thereof in an axial direction, perforated diaphragm screeningmeans extending radially into the grinding zone and carried by the endof the drum having the exit means therein and the inner surface of saidscreening means being exposed to the material undergoing reduction, thecircumferential perimeter of said screening means extending in an axialdirection into the grinding zone beyond the adjacent areas of the endwall and the inner peripheral surface of the drum sloping radiallyoutward from the perimeter of the drum toward the center thereof, andlifter bars extending radially inward from and transversely across saidinner peripheral surface of the drum at spaced circumferentialintervals, said bars having substantially straight inner surfacesexposed to the material undergoing reduction, whereby the greatestlifting area of said bars is substantially in the center of said drumand the inwardly extending circumferential perimeter of said screeningmeans being operable to defiect materia-l falling thereonto away fromsaid diaphragm means to cooperate with said sloping peripheral surfacesof said drum to effect mixing of all size segments of material in atransverse direction within the grinding zone of said drum.

8. A rotatable tumbling mill for treating friable material to reduce thesize thereof and having opposed ends of convex configurations slopingaway from each other from the periphery to the axis of the mill, thediameter of the Vinternal grinding zone of the mill being substantiallygreater than the axial length thereof and the ends of the mill beingprovided respectively with inlet and exit means, annular perforateddiaphragm screening means carried by the end of the mill having the exitmeans therein and spaced from said end in an axial direction, saiddiaphragm means converging substantially radially inwardly from theperiphery of said mill a predetermined distance toward the axis thereofbut spaced therefrom, a circumferential portion of said diaphragmscreening means being substantially parallel to said end of the mill andanother circumferential portion thereof being substantially vertical tothe axis of the mill, and deliecting means adjacent the circumferentialportion of said diaphragm screening means nearest the axis of said milland extending laterally inward from said circumferential portion toeffect defiection of falling material in a direction away from saiddiaphragm means.

9. A rotatable tumbling mill for treating friable material to reduce thesize thereof and comprising a drum having opposed ends respectivelyhaving substantially coaxial inlet and exit means therein, the interiorof the drum comprising a grinding zone the diameter of which 4issubstantially greater than the length thereof in an axial direction,annular perforated diaphragm screening means spaced inwardly in an axialdirection from the end of said drum having the exit means therein andthe inner and outer perimeters of said diaphragm means respectivelybeing spaced from the axis and the peripheral surface of the grindingzone, there being an annular grinding space of predetermined appreciableradial depth defined by the periphery of the mill and the outerperimeter of said diaphragm means, and substantially annular detlectingmeans extending respectively around said perimeters of said diaphragmmeans and at least one of said deecting means projecting into said drumaxially beyond the inner surfaces of said diaphragm screening means andsaid deecting means being operable to deflect material from directfalling impact with said diaphragm surface, thereby minimizing abrasionof said grate means and effecting transverse mixing of the materialundergoing treatment.

10. A rotatable tumbling mill for treating friable material to reducethe size thereof and having opposed ends of convex configurationssloping away from each other from the periphery to the axis of the mill,the diameter of the internal grinding zone of the mill beingsubstantially greater than the axial length thereof and the ends of themill being provided respectively with inlet and exit means, annularperforated diaphragm screening means carried by the .exit end of themill and spaced in an axial direction into the mill and at leastportions of said screening means being substantially parallel to theadjacent convex ends of the mill, the inner and outer perimeters of saiddiaphragm means respectively being spaced from the axis and theperipheral inner surface of said mill, deflecting substantially annularmeans respectively extending around the perimeters of said diaphragmmeans and projecting in an axial direction into the grinding zone of themill respectively beyond the adjacent perimeter of said diaphragm meansand said deflecting surfaces being operable to be engaged by fallingmaterial to deflect the same away from said diaphragm screening means toprotect the same and also minimize stratification of material withinsaid grinding zone.

11. A rotatable tumbling mill for treating mixtures of various sizes offriable material to reduce the same to a predetermined range of finesizes thereof by self-reduction of all sizes simultaneously andcomprising a drum having opposed ends and the diameter of the internalgrinding zone of the mill being substantially greater than the axiallength thereof, the ends of the mill being provided respectively withsubstantially coaxial inlet and exit means, substantially annular andradially extending perforated diaphragm screening means carried by theexit end of the mill to define at least a portion of one end of thegrinding zone within the mill, means comprising a set of material liftermeans having a predetermined height and detachably connectable relativeto the inner surface of the mill in directions substantiallyperpendicular thereto and perable to provide the mill with a certainlifting effect upon a given run of material and produce a determinablerate of reduction of material within the mill, additional sets ofmaterial lifter means respectively having heights different from eachother and the predetermined height of said aforementioned set, said setsselectively being exchangeable one for the other respectively to producedifferent lifting effects within the mill if said determinable rate ofreduction of said given run of material is not a desired optimum, andmeans to connect a selected set of said material lifter means detachablyto the interior of the mill in spaced relationship to each other,whereby a selected set of said material lifter means of a given heightmay be exchanged for another set of material lifter means of a differentheight to produce an optimum reduction rate of a given run of materialwithin the mill.

l2. A rotatable tumbling mill for treating mixtures of various sizes offriable material to reduce the sizes thereof to a predetermined range offine sizes thereof and comprising a drum having opposed endsrespectively provided with substantially coaxial inlet and exit meanstherein, perforated diaphragm screening means carried by the exit end ofthe mill and extending radially, the perimeter of said diaphragmscreening means being spaced from the interior periphery of the drum andthe interior surface of the end of the mill carrying said diaphragmscreening means being positioned axially outward from said diaphragmscreening means to provide a substantially annular expanded zone withinthe drum adjacent the periphery thereof, and radial lifter barsconnected to the interior surface of said end of the drum incircumferentially spaced relationship to each other within said expandedzone.

13. A rotatable tumbling mill for treating mixtures of various sizes offriable material to reduce the sizes thereof to Ya predetermined rangeof fine sizes'thereof and comprising a drum having opposed endsrespectively provided with substantially coaxial inlet and exit meanstherein, perforated diaphragm screening means carried by the exit end ofthe mill and extending radially, the perimeter of said diaphragm meansbeing spaced from the interior periphery of the drum and the interiorsurface of the end of the mill carrying said diaphragm means beingpositioned axially outward from said diaphragm to provide asubstantially annular expanded zone within the drum adjacent theperiphery thereof, means comprising a set of material lifter means of agiven height connectable detachably against the end wall in saidexpanded zone in circumferentially spaced relationship to each other andoperable to provide the drum with a certain lifting effect in saidexpanded zone relative to a given run of material and thereby produce amixing of the various sizes of material within the drum by action of thelifted material within said expanded zone in being deflected laterallyfrom said zone and thereby produce a determinable rate of reduction,additional sets of material lifter means respectively having heightsdifferent from each other and the given height of said aforementionedset, said sets selectively being exchangeable one for the other toproduce different lifting effects within said expanded zone if saiddeterminable rate of reduction of a given run of material is not adesired optimum, and means to connect a selected set of said materiallifter means detachably to said end wall within said expanded zone,whereby said selected set of said material lifter means of a givenheight may be exchanged for another of said sets of material liftermeans of a different height to produce an optimum lifting effect in saidexpanded zone upon a given run of material to produce thorough mixing ofall sizes of material within the drum as a result of the lifted materialWithin said expanded zone being deflected laterally from said expandedzone and thereby produce an optimum reduction rate of a given run ofmaterial within the mill.

14. A rotatable mill for subjecting a mixture of friable material ofdifferent sizes to reduction to a range of finer sizes within a desiredrange, said mill having ends respectively provided with substantiallycoaxial inlet and exit means and the diameter of the interior of themill being substantially greater than the length thereof in an axialdirection, annular perforated diaphragm screening means carried by theend of the mill having the exit means therein and spaced from said endin an axial direction, said diaphragm means extending substantiallyradially within said mill and defining at least a portion of one end ofthe grinding zone of the mill and operable to permit dischargetherethrough for passage to said exit means of a range of products lessthan a predetermined maximum, guiding and lifting means on the interiorperipheral surface of the mill between the ends thereof, said meanshaving angularly related guiding surfaces on said interior periphery ofthe mill for engagement of the material as tumbled within said mill tocause all sizes of said material to be intermixed and moved in oppositeaxial directions and said guiding and lifting means comprising a set ofmaterial lifter means of a given height detachably connectable relativeto said aforementioned inner peripheral surface of the mill andprojecting inwardly therefrom, said set of means being operable toproduce a certain lifting effect upon a given run of material to producea determinable rate of reduction of material within the mill, additionalsets of material lifter means similar to the aforementioned set but allof said sets respectively having heights different from the other sets,said sets selectively being exchangeable one for the other to producedifferent lifting effects within the mill if said determinable rate ofreduction of a given run of material is not a desired optimum, and meansdetachably connecting a selected set of said material lifter means tothe periphery of said mill to provide the mill with optimum liftingeffect relative to a given run of material.

15. A process of treating run-of-the-mine solid material consisting of amixture of large, intermediate and relatively fine sizes of the materialto grind and reduce all sizes of the same simultaneously andprogressively and autogenously to a predetermined range of fine sizes bytumbling the same within a rotatable mill while thoroughly mixing allsizes by substantially unobstructed transverse movement from end to endwithin the mill in a direction parallel to the axis of rotation of themill, retaining the coarser particles of unwanted sizes for furtherreduction in size, separating the finer sizes of a predetermined rangetherefrom continuously by screening incident to removal from the mill,and further subjecting the retained coarse particles of an unwanted sizeadjacent to the screening zone to additional movement toward and awayfrom said screening zone to enhance the mixing action of the retainedcoarse particles adjacent the screening zone within the mill and therebycause grinding engagement thereof with the other sizes of materialtherein present when the coarse particles are out of contact with thescreening means to facilitate discharge of the desired sufficientlyreduced size ranges when in said screening zone.

16. The method of operating a tumbling mill provided with interiorprotrusions in the comminution of a mixture of ranges of various sizesof friable material autogenously to effect optimum efficiency insimultaneous reduction in size of all sizes of material in said mixtureby the impinging forces of the material acting upon itself and theinterior surfaces of the mill while tumbling, said method comprising thesteps of feeding to said tumbling mill at a selected rate a mixture ofsaid friable material of unknown reduction characteristics andconsisting of coarse sizes mixed with intermediate and fine sizes,grinding said material autogenously within said mill while employingmaterial lifters of a selected contour for a trial period of timesucient substantially to stabilize the material load size range and sizeratios within the mill, determining the reduction characteristics asestablished by said load in the mill, then altering the contour of theinterior of the mill sufficiently to vary the reduction characteristicstherein to produce a size range and ratio of the various size ranges ofthe material load within the mill different from that produced duringthe trial period if said ratio is not substantially that having adesired size range and ratio of said various sizes of material enablingsaid mill to produce a product of the desired characteristics at optimumefiiciency under the existing conditions.

17. The method of operating a tumbling mill as set forth in claim 16 andfurther characterized by said grinding occurring in a confined zonewhile moving the mass of the material axially therein between the endsof the mill to maintain all sizes thereof axially mixed and moving saidmass of the material vertically a substantially greater distance than itis moved axially, and removing said product from a discharge zoneadjacent one end of said mill at a location below the load level in saidmill.

18. The method of operating a tumbling mill provided with interiorprotrusions in the comminution of a mixture of ranges of various sizesof friable material autogenously to effect optimum eiciency insimultaneous reduction in size of all sizes of material in said mixtureby the impinging forces of the material acting upon itself and theinterior surfaces of the mill while tumbling, said method comprising thesteps of feeding to said tumbling mill at a selected rate a mixture ofsaid friable material of unknown reduction characteristics andconsisting of coarse sizes mixed with intermediate and fine sizes,grinding said material autogenously within said mill while employingmaterial lifters of a selected contour for a trial period of timesufficient substantially to stabilize the material load size range andsize ratios within the mill, determining the reduction characteristicsas established by said load in the mill, and altering the contour of themill to cause greater impact of coarse sizes of material for more rapiddisintegration thereof if the ratio of said coarse sizes to the 2f)smaller sizes is determined to be too high for a desired reduction rate.

19. The method of operating a tumbling mill provided with interiorprotrusions in the comminution of `a mixture of ranges of various sizesof friable material autogenously to effect optimum efficiency insimultaneous reduction in size of all sizes of material in said mixtureby the impinging forces of the material acting upon itself and the interior surfaces of the mill while tumbling, said method comprising thesteps of feeding to said tumbling mill at a selected rate a mixture ofsaid friable material of unknown reduction characteristics andconsisting of coarse sizes mixed with intermediate and fine sizes,grinding said material autogenously within said mill while employingmaterial lifters of a selected contour for a trial period of timesufficient substantially to stabilize the material load size range andsize ratios within the mill, determining the reduction characteristicsas established by said load in the mill, and altering the contour of themill to produce a decreased rate of disintegration of the coarse sizesof material if the ratio of smaller sizes of material to the coarsesizes thereof is determined to be too high for a desired reduction rate.

20. A process of treating run-of-the-mine solid material consisting of amixture of large, intermediate and relatively fine sizes of material togrind and reduce all sizes of the same simultaneously and progressivelyand autogenously to a predetermined range of fire sizes by tumbling thesame within a rotatable mill having a diameter substantially greaterthan the length thereof while thoroughly mixing all sizes by substantialtransverse movement from end to end within the mill in a directionparallel to the axis of rotation of the mill, retaining the coarserparticles of unwanted sizes for further reduction in size, andseparating the finer sizes of a predetermined range therefromcontinuously by screening adjacent the location of maximum impact offalling pieces of material and facilitating the removal of said finersizes from the mill by said mixing action in a direction parallel to theaxis of rotation of the mill serving constantly to move the coarserparticles of material away from the screening zone to free the same forsaid finer sizes to discharge therethrough.

2l. A rotatable tumbling mill for treating friablle material to reducethe size thereof and having opposed ends, the diameter of the internalgrinding Zone of the mill being substantially greater than the axiallength thereof and the ends of the mill being provided respectively withinlet and exit means, annular perforated diaphragm screening meanscarried by the end of the mill having the exit means therein and spacedfrom said end in an axial direction, said diaphragm screening meansextending radially substantially from the periphery of said mill apredetermined distance toward the axis thereof, whereby screening of thematerial for discharge of a range of sizes less than a predeterminedmaximum may occur adjacent the location of maximum impact of fallingmaterial, and means within the mill and movable therewith for engagementby falling material as the mill rotates and operable to effect mixingmovement of the various sizes of material in directions extendingaxially of the mill.

22. The -mill set forth in claim 2l further characterized by said meansto effect mixing movement including annular defiector means adjacent theinner periphery of said screening means and operable to dcfiect materialfrom direct falling impact with said screening means, thereby, tominimize abrasion of said means.

23. The mill set forth in claim 22 further including end Wall meanswithin said annular deflector means and extending radially toward theaxis of said mill, said end wall means retaining within the mill thematerial undergoing reduction within the zone of the mill adjacent saidend wall means.

24 The mill set forth in claim 2l further characterized 21 by said meansto effect mixing movement including variations in the contour of theinner surface of at least one end wall of said mill arranged so as to beengaged by all sizes of said material being treated within the mill andsaid means also being shaped so as to be capable of. eectinginter-mixing and axial movement of all sizes of the material forsubstantially the full length of the mill.

25. The mill set forth in claim 21 further characterized by said meansto effect mixing movement including variations in the contour of theinterior peripheral surface of the mill comprising augularly relatedguiding surfaces extending generally transversely across substantiallythe full width of said peripheral surface and engagea-ble by saidmaterial as tumbled within said mill to cause all sizes of said materialto be intermixed and moved axially in opposite directions.

26. A rotatable tumbling mill for treating friable material to reducethe size thereof and having opposed ends, the diameter of the internalgrinding zone of the mill being substantially greater than the axiallength thereof and the ends of the mill being provided respectively withinlet and exit means, the exit end of the mill having size- 4limitingdischarge opening means therein operable to permit passage therethroughof material of a predetermined maximum size while retaining material oflarger size within the mill for further reduction in size, and annulardeilector means adjacent said size-limiting discharge opening means andengageable by material being tumbled within the mill while falling fromor toward said sizelimiting discharge opening means and operable todeflect said falling material away from said size-limiting dischargeopening means, thereby to minimize abrasion of said means and alsoeffect Imovement of said material substantially axially within saidmill.

27. A rotatable tumbling mill for treating friable material to reducethe size thereof and having opposed ends, said mill having an interalgrinding zone which is substantially unobstructed between the oppositeperipheral surfaces and the diameter of said internal grinding zonebeing substantially greater than the axial length thereof, the ends ofthe mill respectively having inlet and exit means, diaphragm meanshaving size-limiting discharge opening means carried by the end of themill having the exit means therein and spaced from said end in an axialdirection, said discharge opening means extending radially apredetermined distance toward the axis of the mill and permittingdischarge therethrough of a range of sizes of material of apredetermined maximum size from the grinding zone of the mill at a levelsubstantially below the level of discharge of material through the exitin said end of the mill, and means detachably connected to the interiorof the ends of the mill and movable therewith and positioned to beengaged by material falling within the substantially unobstructedinterior portion of the mill as it rotates and deflected thereby toeffect mixing of all sizes of the material axially in oppositedirections substantially from one end of the mill to the other.

References Cited in the file of this patent UNITED STATES PATENTS928,967 Hardinge July 27, 1909 1,080,768 Marcy Dec. 9, 1913 1,222,184Cole Apr. 10, 1917 1,282,914 Mitchell et al Oct. 29, 1918 1,295,726Garrow Feb. 25, 1919 1,315,025 Lawler Sept. 2, 1919 1,335,269 Ball Mar.30, 1920 1,451,472 Pomeroy Apr. 10, 1923 1,589,741 Bonnot et al June 22,1926 l1,591,938 Harrison July 6, 1926 1,690,493 Marcy Nov. 6, 19281,690,495 Marcy Nov. 6, 1928 1,690,497 Willard Nov. 6, 1928 2,185,960Vogel-Jorgensen Jan. 2, 1940 2,381,351 Hardinge Aug. 7, 1945 2,555,171Weston May 29, 1951 2,566,103 Weston Aug. 28, 1951 2,678,167 Weston May11, 1954 FOREIGN PATENTS 118,840 Sweden May 20, 1947 272,033 SwitzerlandMar. 1, 1951 OTHER REFERENCES Hardinge Company, Bulletin 18-A, page 8.Mineral Industry, volume 47, page 682 (1938).

1. A ROTATABLE TUMBLING MILL FOR TREATING FRIABLE MATERIAL TO REDUCE THESIZE THEREOF AND HAVING OPPOSED ENDS OF CONVEX CONFIGURATIONS SLOPINGAWAY FROM EACH OTHER FROM THE PERIPHERY TO THE AXIS OF THE MILL, THEDIAMETER OF THE INTERNAL GRINDING ZONE OF THE MILL BEING SUBSTANTIALLYGREATER THAN THE AXIAL LENGTH THEREOF AND THE ENDS OF THE MILL BEINGPROVIDED RESPECTIVELY WITH INLET AND EXIT MEANS, PERFORATED SCREENINGMEANS CARRIED BY THE EXIT END OF THE MILL AND EXTENDING SUBSTANTIALLYRADIALLY INTO THE GRINDING ZONE OF THE MILL AWAY FROM THE EXIT MEANS ONSAID END, THE INNER SURFACE OF SAID SCREENING MEANS BEING EXPOSED TO THEMATERIAL UNDERGOING REDUCTION AND THE OUTER PERIPHERY OF SAID SCREENINGMEANS BEING SPACED INWARDLY FROM THE OUTER PERIPHERY OF THE GRINDINGZONE OF THE MILL, AND DEFLECTING MEANS ADJACENT THE OUTER PERIPHERY OFSAID SCREENING MEANS HAVING A SUBSTANTIALLY ANNULAR DEFLECTING SURFACEEXTENDING ANGULARLY INWARD AWAY FROM THE EXIT END OF THE MILL CONTIGUOUSTO SAID SCREENING MEANS AND TOWARD THE AXIS OF ROTATION OF THE MILL,SAID ANNULAR DEFLECTING SURFACE BEING OPERABLE TO BE ENGAGED BY MATERIALFALLING WITHIN THE MILL AND DEFLECT THE SAME AWAY FROM SAID SCREENINGMEANS TO PROTECT THE SAME AND ALSO TO PRODUCE AN ADDED INTERMIXINGACTION UPON SAID MATERIAL WITHIN SAID GRINDING ZONE.